The ability to inhibit fertilization by a rationally designed drug that interferes with sperm-egg binding would most likely lead to a new type of contraceptive and be a major contribution to reproductive health. The contraceptive might consist of chemically and/or enzymatically synthesized egg-surface oligosaccharides linked together at high density, as sperm-egg binding in higher vertebrates is mediated by the interaction between a carbohydrate-binding protein located on the surface of the sperm and a specific oligosaccharide side chain of a unique protein located on the surface (zona pellucida) of the egg. The structure of the egg surface oligosaccharide that is recognized by the sperm is not known, other than it contains at least one terminal N-acetylglucosamine residue. We have recently obtained 200 mg of oocyte preparation that will enable us to continue our analyses. Knowledge of the oligosaccharide structure(s) necessary for the binding of mouse sperm to egg will allow us to develop inexpensive inhibitory compounds that can provide an effective, inexpensive pharmaceutical for human contraception.